How long before ice melt affects coastal cities? The Greenland ice sheet is melting and contributing to sea level rise — scientists are certain about that. What they're not sure about is exactly how fast it's happening. That's where NASA's Oceans Melting Greenland mission comes in.

The OMG mission will help scientists put a more precise timeline on sea level rise. They're focusing their attention on Greenland because its ice sheet is the largest global contributor to rising seas. If the entire Greenland ice sheet melts, sea level would rise by an estimated 20 feet. That's enough to flood or submerge much of the world's coasts.

Global warming has caused ocean temperatures around Greenland to increase. The OMG project is measuring the effects of that warm water on ice melt. When data collections wrap up in 2020, NASA scientists will be able to project the rate of sea level rise forward to 2100.

Those projections could help coastal communities plan for sea level rise. It could also be a wake-up call for governments that aren't prepared to deal with consequences like soil and water contamination, flooding and wildlife displacement.